Sass function to produce linear percentage change between two points defined in calc() - sass

Question

I developed an sass function (written in scss) that produces a calc function that changes distance linearly between two given points. This is useful if I want a distance to change smoothly between two breakpoints. The function looks like this and is made to only support pixel values:
#function resp-px($point-a, $point-b){
// Example input: ( "desktop": 50, "tablet": 20 ) produces these values for our variables:
$devices: (
"desktop": 1920,
"laptop": 1280,
"tablet": 1000,
"mobile": 750,
);
$a-width: if(
is-device(first-key-in-map($point-a)),
map-get($devices, first-key-in-map($point-a)) / 100,
first-key-in-map($point-a) / 100
);
$a-pixels: first-value-in-map($point-a);
$b-width: if(
is-device(first-key-in-map($point-b)),
map-get($devices, first-key-in-map($point-b)) / 100,
first-key-in-map($point-b) / 100
);
$b-pixels: first-value-in-map($point-b);
// The example input produces these values for our variables:
// $a-width = 19.2, $a-pixels = 50, $b-width = 12.8, $b-pixels = 20
// We have a system of equations with 2 unknowns: { 19.2a + b = 50, 12.8a + b = 20 }
// Solution step by step:
// a = (50 - b)/19.2
// b = 20 - 12.8a => 20 - 12.8((50 - b)/19.2) = 20 - 12.8(50/19.2 - b/19.2) =
// = 20 - ((50 * 12.8) / 19.2 - (b * 12.8) / 19.2) = 20 - (50 * 12.8 / 19.2 - b * 12.8 / 19.2) =
// = 20 - 50 * 12.8 / 19.2 + b * 12.8 / 19.2
// => b - b * 12.8 / 19.2 = 20 - 50 * 12.8 / 19.2
// => (b - b * 12.8 / 19.2) * (1 / (1 - 12.8 / 19.2) = (20 - 50 * 12.8 / 19.2) * (1 / (1 - 12.8 / 19.2)
// => b = (20 - 50 * 12.8 / 19.2) * (1 / (1 - 12.8 / 19.2)
// && a = (50 - b)/19.2
$m: ($b-pixels - $a-pixels * $b-width / $a-width) * (1 / (1 - $b-width / $a-width));
$k: ($a-pixels - $m)/$a-width;
#return calc(#{$k}vw + #{$m}px);
}
Now, however, I want to support percentage values for the distance as well. BUT... I cannot wrap my head around how this can be done. Anyone got a solution? Can be a separate function as well if it makes it easier (named "resp-percentage" for example).
Tried including $b-pixels / 100 and $a-pixels / 100 in the equation but didn't get a solution.